1. Field of the Invention
The present invention relates to an illumination apparatus and a projection display device, which utilize fourth color component light in addition to red component light, green component light, and blue component light.
2. Description of the Related Art
Conventionally, a projection display device has been known, which provided with light valves corresponding to three colors, a cross dichroic cube that combines lights emitted from the three light valves, and a projection mean that projects a light combined by the cross dichroic cube.
Herein, the cross dichroic cube has three light incident surfaces which light enters and one light-emitting surface from which light is emitted. Accordingly, in the case of using three colors of light to be incident on the cross dichroic cube, it suffices that the projection display apparatus has one cross dichroic cube.
On the other hand, for the purpose of improving color reproduction capability and luminance, there has been proposed a projection display apparatus using four or more colors of light. By using, for example, orange, yellow, or cyan light in addition to three colors of red, green, and blue light, such a projection display apparatus is intended to improve color reproduction capability and luminance (for instance, see Japanese Patent Publication No. 2002-287247 (claims 1 and 4, FIG. 1, and the like)).
When lights of four colors or more are utilized in the projection display apparatus, lights of four colors or more cannot be combined by one cross dichroic cube. For this reason, the projection display apparatus should be provided with a plurality of dichroic cubes (or cross dichroic cubes).
For example, when a combination of lights of four different colors is needed, the projection display apparatus obtains two combined lights in each of which lights of two different colors are combined, and further combines the two combined lights to obtain a combined light of four different colors. In addition, the projection display apparatus may obtain a combined light in which lights of three different colors are combined and combine the obtained light with one color light to obtain a combined light of four different colors. Moreover, the projection display apparatus may obtain a combined light in which lights of two different colors are combined and combine the obtained light with color lights of two different colors to obtain a combined light of four different colors.
Here, an optical path length from each of the light valves corresponding to four or more colors to the projection mean should be the same. Moreover, there is need to provide a plurality of dichroic cubes (or cross dichroic cubes) between the light valves and the projection mean. Accordingly, the back focus of the projection mean becomes longer.
As a result, a projection mean used in a projection display apparatus using light of three colors cannot be used for the one using light of four or more colors, leading to an increase in manufacturing cost of the projection display apparatus as a whole.